Capacitive micromachined ultrasonic transducer (CMUT) devices are becoming increasingly popular in medical applications. For example, CMUT devices have been used to improve medical ultrasound imaging probes. CMUT devices have also been used to provide high-intensity focused ultrasound for use in medical therapy. Conventional CMUT devices are typically produced directly on a silicon substrate (i.e. on a silicon wafer). For instance, conventional CMUT devices are often fabricated using a micro-electro-mechanical system (MEMS) manufacturing technique in which a release layer is etched out, leaving a free-standing (flexible) membrane. The top of the membrane is metalized to provide a top (electrode) plate, and the membrane is then used as a transducer to transmit and receive ultrasonic signals.
Conventional CMUT devices utilize bond pads to provide electrical contact to the top plate for each of the CMUT elements in the device, such as a plurality of bond pads for a CMUT device including a plurality of CMUT elements arranged in a CMUT array. Since the bond wire is elevated above the bond pad, the bond pad is placed remote from the CMUT elements in the CMUT array to facilitate packaging. This constraint not only increases the CMUT device die size due to the need for interconnect routing lines, but it also complicates the packaging process. Both the increased die size and the complicated packaging process increase the cost of packaged CMUT die.